Susan Hawkins walks to her apartment from the Spring Center strip mall that sits on 16th Street near downtown Silver Spring. The state of Maryland could buy the property to make way for the 16-mile Purple Line. (Jahi Chikwendiu/The Washington Post)

Building a light-rail Purple Line across the Maryland suburbs would require condemning 116 homes and businesses and cutting down most trees on a popular walking and biking path between Bethesda and Silver Spring, according to a final environmental study released Thursday.

The 16-mile line between Bethesda and New Carrollton would also bring noticeable noise to some communities because trains would have to sound warning horns or bells as they approached intersections. Some residents also would feel vibrations from passing trains, the study found.

However, the study spells out in the most detail yet the broader impact on people within 500 feet of the planned route, both during construction and once trains began passing by 70 times a day.

Of the 116 displacements, 53 would be houses or apartment units, and 60 would be businesses that have an estimated total of 246 employees. Most of the affected businesses are in Silver Spring and Takoma Park, including several in the Mega Super Market on University Boulevard.

Three “institutional properties” would be condemned, including the Silver Spring post office on 16th Street.

The biggest effects would be felt in the Riverdale area of Prince George’s County, where 22 homes would be lost along Riverdale Road. State officials said most of the residents asked that the project take their entire properties rather than leave them living closer to the busy road and a train line.

Residents along Wayne Avenue east of downtown Silver Spring would lose strips of front yards to road widening and would hear significant construction noise, particularly during 30 months when a tunnel three-tenths of a mile long would be blasted and built between Wayne and Arliss Street, the MTA report says.

Two six-unit apartment buildings above the tunnel’s designated location would be torn down, the report says.

After a Purple Line began to operate, some residents also might hear the “hum” of 18 electrical substations that would be spaced about a mile apart along the route. The trains would be powered by overhead electrical wires.

MTA spokesman Terry Owens said the study outlines “potential” impacts, identified based on early engineering, and could be reduced during final design.

Although densely populated communities are necessary to make a rail line cost-effective, state transit planners have said threading a Purple Line through developed areas inside the Capital Beltway would be challenging.

The line would connect the Maryland ends of the Metrorail system with Amtrak and commuter rail (MARC) stations. State transit officials say it would provide faster, more reliable east-west transit than buses and spur redevelopment near stations.

A rush-hour ride between Bethesda and New Carrollton that now takes 92 minutes by bus would take 63 minutes on a Purple Line, the study found.

Many of the neighborhood impacts would stem from road widening required to accommodate trains in their own lanes. The line would run primarily aboveground and along local roads.

Driveways and sidewalks would have to be moved at some churches and schools, including Silver Spring International Middle School on Wayne Avenue. Other schools that could be disrupted during construction include Rosemary Hills Elementary School and Sligo Creek Elementary School, the report says.

The University of Maryland’s signature “Big M” logo also would be moved as part of rebuilding Campus Drive to allow for dedicated train lanes.

Land from 315 parcels would be condemned temporarily to provide easements during construction for equipment storage, drainage and other purposes.

The report does not include addresses of property owners whose land or buildings would be condemned or those that would hear the most noise. However, it says people in seven houses and four apartment buildings would hear “moderate” noise.

Several sites on the western end of the line — two houses on East-West Highway, two houses on Edgevale Court and a six-unit building at the Barrington Apartments on Rosemary Hills Drive — would feel vibrations above federal thresholds, the report says.

The state would develop unspecified “appropriate mitigation measures” to reduce vibrations, the report says.

Train noise also would affect the popular Georgetown Branch trail, an extension of the Capital Crescent trail. A four-foot sound wall would be built between Bethesda and Rock Creek Stream Valley Park, where the trail runs adjacent to back yards.

Even so, the study found, trains would have a “high level of visual impact” on the trail.

“Much of the existing vegetation would be removed, and most of the existing tree canopy would be eliminated,” the report says.

The federally required environmental review, which took four years, updated forecasts made by a draft study in 2008. The line was then predicted to cost $1.6 billion in 2007 dollars and to attract 68,100 riders a day by 2030. The new study estimates the construction costs at $2.15 billion in “year-of-expenditure” dollars and daily ridership at 74,160 in 2040. The ridership increase stemmed from anticipated population and job growth, officials said.

The line, which would have 21 stations, would cost $38 million annually in 2012 dollars to operate and maintain, according to the updated study. State officials have said they hope to begin construction in 2015 and open the line by 2020.

The public has 30 days to comment on the study before the state submits it to the Federal Transit Administration for approval. Copies are available at www.purplelinemd.com and at libraries in Montgomery and Prince George’s counties.

The FTA’s approval of the environmental review would allow the state to fine-tune the Purple Line’s design and begin condemning and buying private property.

Katherine Shaver is a transportation and development reporter. She joined The Washington Post in 1997 and has covered crime, courts, education and local government but most prefers writing about how people get — or don’t get — around the Washington region.

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